Furic, K.

Gajovic, A.

Maljkovic, M.

Music, S.

Schlögl, R.

Su, D.

English

MPG.PuRe

Microstructure and morphology of thermochemically formed IrO<sub>2</sub> and Ir

Microstructure and morphology of thermochemically formed IrO2 and Ir  A. Gajovića, K. Furića, D. Sub, R. Schlögelb, S. Musića, M. Maljkovića   aRuđer Bošković Institute, P.O. Box 180, HR-10002 Zagreb, Croatia bFritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin  Over the past several years, the researchers and engineers focused on the synthesis of IrO2 thin films or IrO2 powders and on the investigation of their properties. IrO2 thin films and powders are characterized with specific physical and chemical properties, which made them suitable for the application in advanced technologies, for example, as electrode materials for the production of components in advanced memory technologies. IrO2 combines high chemical inertness and ohmic conductivity comparable to that of common metals. IrO2-based resistors were made for application in piesoresistive sensors. IrO2-Ta2O5 and IrO2-RuO2 coated electrodes have found application in electrochemistry. The physical and chemical properties of IrO2 thin films and powders strongly depended on the route of their synthesis. In other words, controlling the route and parameters of the IrO2 synthesis, it is possible to pronounce some physical or chemical property which is important for specific application of IrO2. The present work focuses on the formation of IrO2 powder by the thermal treatment of iridium(IV)-oxide dihydrate (IrO2 ⋅ 2H2O) or iridium(III)-acetylacetonate (Ir(acac)3).  The formation of IrO2 and Ir by thermal decomposition of IrO2 · 2H2O and Ir(acac)3 in air ambient has been investigated by Raman Spectroscopy (RS), Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED).   Starting material, IrO2 ⋅ 2H2O was amorphous, as found by XRD [1]. SAED pattern of that sample furthermore evidenced the presence of amorphous material (Fig. 1). Raman spectrum of IrO2 ⋅ 2H2O showed two broad bands at 708 cm-1 and 544 cm-1. An additional broad band at 352 cm-1 was interpreted in sense of poor crystallinity and/or presence of very fine particles that tend to periodic aggregation. The aggregation was also documented by TEM as shown in Fig. 1. Upon the heating of the IrO2 · 2H2O at 600 °C the band at 352 cm-1 disappeared. At 600 °C, nanosized IrO2 particles with layered microstructure were formed (Fig. 2). The crystallites of IrO2 had mainly the parallelepiped-like shape and sizes were about 30 nm.   Ir(acac)3 decomposed in air at 200 °C, yielding Ir and traces of IrO2. An increase of heating temperature leads to an increase in IrO2 fraction. A gradual increase in crystallite size of Ir from 11(3) to 30(7) nm with change of temperature from 200 to 500 °C and increase crystallite size of IrO2 from 12(4) to 20(5) nm with change of temperature from 350 to 550 °C were estimated by Scherrer method [1]. Raman bands of IrO2 at 718 and 546 cm-1 were observed (Fig. 3). These wave numbers are smaller than those of IrO2 single crystal. The crystallite sizes of formed materials, revealed in high resolved TEM images, were about 10 nm. Heating temperature of 550 °C enhanced IrO2 fraction and induced grouth of crystallite sizes of both IrO2 and Ir. At the same temperature thin Ir metal films were separately formed.  The results of present study showed that nanosize IrO2 particles can be produced by thermal treatment of amorphous IrO2 ⋅ 2H2O and Ir(acac)3 in air.   [1]  S. Musić, S. Popović, M. Maljković, Ž. Skoko, K. Furić, A. Gajović, “Some factors influencing thermochemical formation of IrO2 and Ir”, Materials Letters 57 (2003) 4509– 4514.      Figure 1: TEM and SAED pattern                  of amorphous IrO2 ⋅ 2H2O                 particles.    Figure 2: Nanosize IrO2 particle                 obtained by heating                 IrO2 ⋅ 2H2O at 600 °C.  Figure 3: Room temperature Raman spectra of      IrO2, prepared by heating Ir(acac)3.       Temperature of IrO2 preparation are      denoted above spectra. 

Microstructure and morphology of thermochemically formed IrO<sub>2</sub> and Ir

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